1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to wireless communication devices used in such wireless communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
In an ideal situation, the overall magnitude and frequency response of the receiver has a desired and predictable response that matches the filtering of the transmitter. For instance, for transceivers that employ phase shift keying (PSK) and/or frequency shift keying (FSK), an ideal in-band frequency response is that of a root raised cosine (RRC) filter, which enables the receiver to sample transmitted symbols without inter-symbol interference and hence optimize the transceiver's resistance towards noise and interferers. In practice, a square root raised cosine filter (SRRC) is employed in the transmitter and an identical filter is employed in the receiver to achieve the RRC filtering. This allows for bandwidth the limitations of the transmitted signal typically called for by communications standards. For instance, a version of the Bluetooth standard dictates that the bandwidth of a channel is 1 MHz with attenuation of −20 dB at the edges of the channel. To achieve the bandwidth limitations, the transmitter includes a pulse shaping filter that essentially removes the sharp edges of digital data transitions (e.g., 0 to 1, 1 to 0), but adversely affects the overall desired responses.
Therefore, a need exists for a programmable equalizer that may be used in the receiver and/or transmitter to approximate desired responses in bandwidth limited applications.